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NIST Corner: The Nose Knows

Matt Staymates, a mechanical engineer at the National Institute of Standards and Technology (NIST), uses a schlieren imaging system to visualize the flow of vapors into an explosives detection device fitted with an artificial dog nose that mimics the “active sniffing” of a dog. Photo by Robert Rathe

In an effort to improve devices that are used to detect explosives, narcotics, and other contraband, a group of government and university scientists found inspiration in nature. Dogs are renowned for their ability to detect chemical odors, and when following a scent, they inhale and exhale roughly five times per second. Most commercial chemical detectors use continuous suction, but in a study described in the journal Scientific Reports, researchers outfitted such a device with a mechanical system that mimics the “active sniffing” of a dog. This modification increased the device’s performance by up to a factor of 10.

“The dog is an active aerodynamic sampling system that literally reaches out and grabs odorants,” explained Matthew Staymates, a mechanical engineer and fluid dynamicist at the National Institute of Standards and Technology (NIST). “It uses fluid dynamics and entrainment to increase its aerodynamic reach to sample vapors at increasingly large distances. Applying this bio-inspired design principle could lead to significantly improved vapor samplers for detecting explosives, narcotics, pathogens—even cancer.”

Trace detection devices now used at points of entry and departure such as airports and seaports, and other sensitive locations, typically employ passive sampling. Examples include equipment that requires swabbing hands or other surfaces and then running the sample through a chemical detector—typically an ion mobility spectrometer. Wand-like vapor detectors accommodate more sampling mobility, but unless the detector scans immediately above it, the chemical signature of a bomb-making ingredient will go unnoticed.

Aiming to uncover clues on how to improve trace detection capabilities, Staymates and colleagues from NIST, the Massachusetts Institute of Technology’s Lincoln Laboratory, and the U.S. Food and Drug Administration reviewed previous studies of dogs to identify what occurs during sniffing. Five times a second, dogs exhale to reach out, pull, and then inhale to deliver a nose full of aromas for decoding by some 300 million receptor cells.

Following nature’s lead, the researchers replicated the external features of a dog’s nose using a 3D printer, with the model based on high-resolution magnetic resonance imaging scans of a female mixed-breed Labrador retriever. The researchers also built a sniffing system using a piston/cylinder mechanism set to a sniff frequency of 5Hz and an airflow rate typical of a Labrador retriever. Because they were mainly interested in reproducing the fluid dynamics that occur outside a dog’s nose, their device did not include the complex interior structures of a real dog’s nose.

With schlieren imaging—a technique widely used in aeronautical engineering to view the flow of air around objects—and high-speed video, the team first confirmed that their imitation nose could indeed sniff much like the real thing, a property documented in previous studies of live dogs.

With each sniff, air jets exit from both nostrils, moving downward and outward. Though it might seem counterintuitive, the air jets entrain—or draw in—vapor-laden air toward the nostrils. During inhalation, the entrained air is pulled into each nostril.

Studies of dogs reveal that five times each second, they exhale to reach out, pull, and then inhale to deliver a nose full of aromas for decoding by some 300 million receptor cells. Researchers replicated the external features of a dog's nose using a 3D printer, and then built a sniffing system using a piston/cylinder mechanism set to a sniff frequency of 5Hz and an airflow rate typical of a Labrador retriever.

The team’s first set of experiments compared the air-sampling performance of their “actively sniffing” artificial dog nose with that of trace-detection devices that rely on continuous suction. The head-to-head comparison with an inhalation system used with a real-time monitoring mass spectrometer found that sampling efficiency with the sniffing artificial dog nose was four times better 10 centimeters (3.9 inches) away from the vapor source and 18 times better at a stand-off distance of 20 centimeters (7.9 inches).

Based on those results, the team outfitted a commercially available vapor detector with their bio-inspired, 3D-printed inlet that sniffed like a dog, rather than inhaling in 10-second intervals, the device’s normal mode of operation. The switch resulted in an improvement in odorant detection by a factor of 16 at a stand-off distance of 4 centimeters (1.6 inches).

“Their incredible air-sampling efficiency is one reason why the dog is such an amazing chemical sampler,” Staymates said. “It’s just a piece of the puzzle. There’s lots more to be learned and to emulate as we work to improve the sensitivity, accuracy and speed of trace-detection technology.”

FINGERPRINT EVIDENCE went through a nearly three-year ordeal in the New Hampshire court system, but eventually emerged unscathed. On April 4, 2008, the New Hampshire Supreme Court unanimously reversed the decision of a lower court to exclude expert testimony regarding fingerprint evidence in the case of The State of New Hampshire v. Richard Langill. The case has been remanded back to the Rockingham County Superior Court.